Children grow up in environments saturated by human-made objects. These artifacts are crucial to our lives not only as tools, but also as an ever-present source of social information: Adults form quick and accurate judgments about another person's traits, interests, and social affiliations simply from the artifacts they own, wea and carry. Yet in spite of the role artifacts play in providing social information in adulthood, th cognitive and developmental bases of social reasoning from artifacts remain unexplored. The proposed research aims to characterize the development of artifact-based social reasoning, in both typically-developing (TD) children and children with Autism Spectrum Disorder (ASD). Through two specific aims, the proposed experiments will explore the development of reasoning about (1) shared interests and (2) shared social history on the basis of artifacts. In the first study, TD and ASD participants will be shown four characters, and an artifact owned by each. The overall functional and perceptual similarity of pairs of these artifacts will be manipulated in order to determine whether children use such similarity to infer shared interests of the characters, and whether they rely on simple heuristics or more complex reasoning processes to do so. A second experiment will examine a more complex inference (shared social history), asking whether TD and ASD children infer that social transmission has occurred when two individuals coincidentally create similar non-functional (decorative) features. In this study, participants will be shown that two people created an artifact with the same features. By specifically manipulating whether the tool's features are seen as decorative or functionally necessary, this design will determine whether and when children draw conclusions about social transmission and shared social history, and do so through high-level reasoning processes, not similarity-based heuristics. The proposed studies are complementary, and provide a low-risk entry point into a novel and important domain. Each specific aim will first test adults and TD children, then compare a matched sample of children with ASD, to determine whether the social difficulties of children with ASD may be in part due to deficits in artifact-based social reasoning By explicitly understanding artifact-based reasoning processes and identifying deficits in the ASD population, this work may lead to new, effective intervention programs to help ASD individuals use information from artifacts to identify appropriate social partners and conversation topics of mutual interest. In addition, the proposed studies will make a significant contribution t our understanding of social cognitive development by characterizing the cognitive processes underlying this social reasoning, and by opening for exploration further questions regarding children's use of social cues from artifacts in their everyday lives.